1. Field of the Invention
This invention is in the field of sampling and culturing microorganisms; more specifically, in the field of replicating cultures of microorganisms.
2. The Prior Art
A microbiologist often needs to replicate a mixed culture of microorganisms which are growing in a petri plate. He/she needs to transfer an inoculum of each and every colony growing on the surface of one plate to the agar surface of a new plate or plates.
A conventional method for accomplishing the transfer uses a round block of wood (or other material) which fits into the petri plate in which the master culture is growing. The bottom of the block is covered with velvet. The (sterilized) velvet-covered surface of the block is gently but firmly pressed against the surface of the master culture; then it is pressed against the agar surface of one or more freshly prepared petri plates. If the procedure is successful, the newly inoculated plates will grow colonies which are exact replicas of the colonies growing in the master culture.
The velvet-covered block procedure has certain drawbacks. Some colonies in the master culture may be raised colonies. Pressing the block against the raised colonies is likely to mash them and spread them out on the velvet, possibly inhibiting the growth on the new plate of neighboring colonies. On the other hand, flat colonies are likely to be bridged over by the velvet, and thereby be absent when the new plate is cultured. Actinomycete colonies, which are quite hard, are often not picked up on the velvet. Finally cleaning and sterilizing the velvet surface after each use quickly destroys the velvet.
A new device (patent pending) for replicating master cultures is being sold under the trade name RepliPlate.TM. by FMC Marine Colloids BiProducts Co. The device, which is disposable, comprises a synthetic sponge fixed into the lid of a conventional petri plate. According to promotional literature on the device ("The RepliPlate.TM. Colony Pad: A New Device for Replicating Microbial Colonies", by Foner P. Curtis and Donald W. Renn) will replicate a plate containing Escherichia coli six times, a yeast, Saccharomyces cerevisiae, four times, and Bacillus subtilis colonies only twice. Although it is disposable, the RepliPlate.TM. suffers from the first three of the disadvantages referred to above for the velvet-covered block.
A need therefore exists for a disposable device which will reliably and repetitively replicate mixed cultures of microorganisms of varying colonial characteristics. Alternatively there is need of such a device which is readily and repeatedly reuseable.